diff --git a/invite.module b/invite.module
index fb961ce..9ec7c57 100644
--- a/invite.module
+++ b/invite.module
@@ -599,7 +599,7 @@ function invite_form_user_login_alter(&$form, &$form_state, $form_id) {
   $invite = invite_load_from_session();
   global $user;
 
-  if ($invite && $invite->status() == INVITE_VALID && (!$invite->invitee || $invite->invitee == $user->uid)) {
+  if ($invite && $invite->status() == INVITE_VALID) {
     $form_state['invite'] = $invite;
     $form['#submit'][] = 'invite_form_user_login_submit';
   }
@@ -633,7 +633,7 @@ function invite_form_user_login_submit($form, &$form_state) {
  */
 function invite_user_insert(&$edit, $account, $category) {
   $invite = invite_load_from_session();
-  if ($invite && empty($invite->invitee) && $invite->status() == INVITE_VALID) {
+  if ($invite && $invite->status() == INVITE_VALID) {
     $invite->invitee = $account->uid;
     $invite->joined = REQUEST_TIME;
     entity_save('invite', $invite);
diff --git a/modules/invite_by_email/invite_by_email.module b/modules/invite_by_email/invite_by_email.module
index bbc95b9..c5114b5 100644
--- a/modules/invite_by_email/invite_by_email.module
+++ b/modules/invite_by_email/invite_by_email.module
@@ -264,7 +264,11 @@ function invite_by_email_invite_presave($invite) {
 
   $entity = entity_metadata_wrapper('invite', $invite);
   $mail_address = $entity->field_invitation_email_address->value();
-  if ($account = user_load_by_mail($mail_address)) {
+  // If the invited email address belongs to a current user, set that user as
+  // the invitee. But don't overwrite the invitee if the invite was already
+  // accepted, because in that case it represents the user account who actually
+  // accepted the invite and therefore should no longer be changed.
+  if (empty($invite->joined) && ($account = user_load_by_mail($mail_address))) {
     $invite->invitee = $account->uid;
   }
   $invite->data['subject'] = $entity->field_invitation_email_subject->value();